DFT / ATPG · All levels
Compression Debug: Comparison Matrix
Comparison Matrix for Compression Debug.
Comparison matrix
Channel count, masking, and compaction trade tester cost and diagnosis precision.
+------------------+----------------+----------------+----------------+
| Approach | Strength | Weakness | Best when |
+------------------+----------------+----------------+----------------+
| Conservative | safe | higher cost | ramp-sensitive |
| Balanced | practical | needs rigor | production |
| Aggressive | fast | escape risk | schedule pressure |
| Architecture | durable | slow | repeated pain |
+------------------+----------------+----------------+----------------+When to choose each approach
Tie approach to product risk and tester constraints
Interview traps
Optimizing one metric only
No regression ownership
Evidence comparison
DFT EVIDENCE MATRIX - Compression Debug
+-------------------+------------------------+--------------------------+-------------------------+
| Evidence | Tells you | Does not prove | Next action |
+-------------------+------------------------+--------------------------+-------------------------+
| coverage report | fault detect trends | silicon root cause | inspect bucket details |
| pattern diff | generation changes | architecture quality | replay suspect patterns |
| timing/power report| test closure margin | diagnosis confidence | correlate fail logs |
| diagnosis summary | likely defect classes | ownership decision | assign action owner |
| signoff checklist | process completeness | correctness of evidence | peer review artifacts |
+-------------------+------------------------+--------------------------+-------------------------+DFT deep dive
Compression saves tester time only when diagnosis observability remains credible.
Concept diagram
COMPRESSION LOOP
EDT/decompressor -> compressed patterns -> compactor responses -> diagnosisMetric graph
PATTERN vs COVERAGE
coverage up -> pattern count up
compression up -> pattern count down (until aliasing risk)Reports and artifacts
compression ratio dashboard
pattern count trend
X-source report
diagnosis bucket summary
Mini case study
Compactor overflow plus unknown inflation caused false diagnosis; masking policy and channel map corrected.
Debug branches
Separate X issues from silicon defects
Replay failing patterns uncompressed
Track tester memory budget
Senior review question
Ask: what evidence proves this DFT decision is safe for production?
Key takeaways
State metric, lot/corner context, and pattern tag with every claim.
Treat timing, power, and quality as one signoff problem.
Common pitfalls
Chasing coverage without legality checks.
Ignoring test-power side effects of pattern changes.
Debugging silicon without reproducible tags.
Principal DFT review addendum
Compression debug isolates whether failures come from EDT wiring, X-masking policy, clocking, or ATPG assumptions before blaming silicon defects.
Metric: unknown/X inflation, compactor overflow incidents, pattern replay success rate